Compute simple pivot table of a CSV file

pivot.php

<?php

if (count($argv) < 4) {
    echo "
Usage: php pivot.php <file> <column>[,<column>] <column>:<func>

Examples:
    php pivot.php data.csv Type sum:Amount
    php pivot.php data.csv Type,Description sum:Amount
";
    exit(1);
}

[$script, $file, $columns, $func] = $argv;

$in = fopen($file, 'r');
$out = fopen('php://stdout', 'w');

$columns = explode(',', $columns);
[$func, $func_column] = explode(':', $func);

$headers = fgetcsv($in);
$pivot = [];
while (true) {
    $data = fgetcsv($in);
    if ($data === false) break;
    $data = array_combine($headers, $data);
    $key = serialize(array_intersect_key($data, array_flip($columns)));
    $pivot[$key][] = $data[$func_column];
}

$header = false;
foreach ($pivot as $key => $values) {
    if (! $header) {
        fputcsv($out, array_merge(array_keys(unserialize($key)), [$func]));
        $header = true;
    }
    // todo: support other functions
    $sum = array_sum($values);
    if (abs($sum) < 0.05) continue;
    fputcsv($out, array_merge(unserialize($key), [$sum]));
}